Thermodynamic analysis of the novel chemical looping process for two-grade hydrogen production with CO2 capture

The integrated sorption-enhanced chemical looping reforming and water splitting (SECLR-WS) process was proposed for hydrogen (H-2) production from biogas using iron oxide as an oxygen carrier and calcium oxide (CaO) as a carbon dioxide (CO2) adsorbent. In the SECLR-WS process, the biogas feed is partially oxidized using iron oxide and CO2 is captured by CaO in the fuel reactor (FR) to produce H-2-rich syngas. The iron oxide is re oxidized in the steam reactor (SR) to generate a high-purity H-2 stream and CaO is regenerated in the calcinator. The simulation of the SECLR-WS process was based on a thermodynamic approach and was performed using an Aspen Plus simulator. The effects of key parameters such as the steam feed to the FR to methane (S-FR/CH4) and iron (II, III) oxide (Fe3O4) to CH4 (Fe3O4/CH4) molar ratios on the process performance in terms of H-2 yield and purity, and CH4 conversion were investigated. The results showed that the H-2 yield, H-2 purity in the FR, and CH4 conversion could be improved by increasing the S-FR/CH4 and CaO/CH4 molar ratios. A total H-2 yield of 3.8 and a H-2 purity in the FR of 97.01 mol% can be obtained at the FR and SR temperatures of 610 and 500 degrees C, and S-FR/CH4, CaO/CH4, Fe3O4/CH4, and S-SR/CH4 molar ratios of 2.2, 1.66, 1, and 2.87, respectively. The molar concentration of carbon monoxide (CO) in the high-purity H-2 stream could be reduced by increasing the pressure in the SR and the amount of CO2 in the biogas feed stream negatively affected the performance of the system. In addition, increasing the Fe3O4/CH4 molar ratio can improve the heat demand in the FR.